Sheet length controller



Sept. 19, 1961 F, s R 3,000,243

SHEET LENGTH CONTROLLER Filed Sept. 9, 1955 5 Sheets-Sheet 1 Fig. I A

WITNESSES PTl \NVENTOR Loren F. Stringer 57 W BY QUJJAZZMA ai/5WATTORNEY Sept. 19, 1961 L. F. STRINGER 3,000,243

SHEET LENGTH CONTROLLER Filed Sept. 9, 1955 5 Sheets-Sheet 2 Fig. IB

444:; I :i7v44 1-{42 39 5 Sheets-Sheet 3 Filed Sept. 9, 1955 Fig. IC

MT i -Riki United States Patent 3,000,243 SHEET LENGTH CONIROLLER LorenF. Stringer, Monroeville, Pa., assignor to Westinghouse ElectricCorporation, East Pittsburgh, Pa., a corporation of Pennsylvania FiledSept. 9, 1955, Ser. No. 533,478 9 Claims. (Cl. 80-56) My inventionrelates generally to motor control systems, and it has reference inparticular to a control system for the screwdown motor of a rolling millfor controlling the length of a sheet of material being rolled.

Generally stated, it is an object of my invention to provide forcontrolling the length of sheets or strips of material being rolled bycontrolling the separation of the rolls in a rolling mill.

More specifically, it is an object of my invention to provide forautomatically operating the screwdown motor of a rolling mill to adjustthe separation of the rolls in accordance with the length of a sheetwhich is to be rolled, so as to produce a rolled sheet of apredetermined length.

Another object of my invention is to provide in a control system for arolling mill for adjusting the separation of the rolls in accordancewith the length of a piece of material which is to be rolled and forchecking the length of the piece after it is rolled, in order to makeadjustments in the roll separation to correct for variations from thedesired length.

It is also an object of my invention to provide for using a servo systemto produce a signal in accordance with the length of a sheet which is tobe rolled, controlling the roll separation in accordance with suchsignal and then using the signal to reset the servo system.

Another object of my invention is to provide in a screwdown controlsystem for a rolling mill, for using a voltage proportional to the speedof a sheet of material entering the rolling mill for operating a servosystem to effect adjustment of the roll separation so as to produce arolled sheet having a predetermined length.

Yet another object of my invention is to provide in a control system fora rolling mill, for controlling the roll separation by means of avelocity matching servo system in accordance with the length of a sheetentering the mill, and for resetting the servo system by utilizing theoutput thereof to return it to an initial position.

It is an important object of my invention to provide in a control systemfor a rolling mill, for operating the mill screwdown to maintain thequotient of initial sheet length over final sheet thickness a constantvalue.

Other objects will in part be obvious and will in part be explainedhereinafter.

In practicing my invention in accordance with one of its embodiments,sheets of a predetermined length are to be produced from sheets ofsubstantially uniform thickness and variable length. For this purpose amagnetic amplifier is used to control the screwdown motor of a rollingmill by utilizing a servo system which is responsive to the speed ofapproach of a sheet of material of finite length which is to be rolledto a predetermined length, for applying to the magnetic amplifier avoltage proportional to the initial length of the sheet. This voltage ismultiplied by a voltage proportional to the initial sheet thickness andthe product is matched against the product of voltage proportional tothe roll separation as determined by a synchro system driven by thescrewdown motor, and a voltage portional to the final sheet length. Thelength of the rolled sheet is then checked by a light responsive lengthchecking system, and a correction factor is applied to the final sheetlength voltage for correcting any deviation from the predeterminedlength. The servo system is reset after the screwdown motor is operatedby feeding its output back into the system to restore it to an initialsetting.

For a more complete understanding of the nature and scope of myinvention, reference may be made to the following detailed descriptionwhich may be read in connection with the accompanying drawings, in whichFIG- URES 1A, 1B and 1C taken together are a schematic diagram of ascrewdown system embodying the principal features of the invention.

Referring to FIG. IE, it will be seen that a rolling mill 10 having workrolls 11 and 12 provided with backup rolls 13 and 14, respectively, isprovided with screwdown means 15 represented by a threaded shaft formoving the upper roll 11 relative to the lower roll 12 for varying theroll separation. The work rolls 11 and 12 may be driven in a well knownmanner by means of a main mill motor MM which may be provided withsuitable controls of a type well known in the art. Conveyor rolls 17 areprovided in conjunction with the rolling mill 10 for feeding a sheet ofmaterial which is to be rolled toward the rolling mill and carrying itaway therefrom after it had been rolled. The conveyor rolls 17 may bedriven in any suitable manner, and since their speed should be matchedwith that of the work rolls 11 and 12, they are shown schematically asconnected in driving relation with the mill motor MM for purposes ofsimplicity.

The screwdown means 15 is provided with a screwdown motor SDM having anarmature 20 connected in driving relation with the screwdown means, aseries field winding 21, and a main separately excited field winding 22which is connected to a suitable source of direct current. Electricalenergy is supplied to the armature 20 of the motor SDM from a screwdowngenerator SDG having an armature 24 which may be driven by any suitableprime mover, a series field winding 25 connected in circuit with thearmature 24, series field winding 21 and armature 20, and oppositelydisposed main field windings 26 and 27 for reversibly controlling theoutput of the generator.

Energization of the field windings 26 and 27 is selectively efiected inopposite senses under the control of a magnetic amplifier 30 whichcomprises a plurality of magnetic cores 31 and 31 arranged in pairs andhaving load windings 32 thereon for selectively connecting the fieldwindings 26 and 27 through rectifier bridges circuits 34 and 35 toalternating current sources represented by the transformers 36. The loadwindings 32 of each pair of cores are connected in parallel circuitrelation, in series with oppositely disposed rectifier devices 38 so asto provide for unidirectional magnetization of the cores. The cores arealso provided with jog windings 39 and 39' which are reversiblyenergizable so as to be cumulative with respect to the respective loadwindings and are connected to a source of direct current through amanual reversing control switch 40 in opposition with the voltage of thearmature 24 of the generator so as to provide for manual control of thescrewdown motor SDM. Feedback windings 42 and 42 are provided on thecores and are connected to a pilot generator PG driven by the screwdownmotor. These windings are difierential with respect to control windings44. Control windings 44 are energized in a manner which will behereinafter described.

Because of the conservation of volume involved in the rolling process, V=L W S V =L W XS where V equals the sheet volume, L equals the sheetlength, W equals the sheet width and S equals the sheet thickness, thesubscript 1 referring to initial conditions and subscript 0 referring tofinal conditions. if

and hence Since initial thickness '8 remains substantially fixed, it isonly necessary to measure the initial length of each sheet and vary thescrewdown setting of the rolling mill and hence vary the final thicknessof the rolled sheet to maintain the quotient constant.

The sheet length can be measured by measuring the length of time ittakes for the sheet which is being transported to the finishing mill onthe conveyor rolls to pass a specified position. A means for doing thisis shown in FIG. 1A. A pair of germanium diode phototransistors PTl andPT2 of the NPN junction type are spaced a distance L which is less thanthe initial length of the sheet, longitudinally of the conveyor rolls 17ahead of the rolling mill on the entry side, in conjunction with lightsources LS1 and LS2, respectively. These transistors are connected inparallel circuit relation, in series with the operating winding of acontrol relay CRL which is normally energized and is deenergized when anapproaching sheet of material 48 moving toward the rolling mill on rolls17 interrupts both of the light sources. A velocity matching servosystem 50 is used in conjunction with a relay CRL to operate the movablecontact Pla of a potentiomettr P1, for providing a voltage c inaccordance with the length of the sheet.

The servo system 50 comprises a two-phase servo motor SM which drivesthe moving contact Fla. The motor SM is provided with one phase winding51 which is energized from an alternating current source represented bya transformer 52 through a capacitor 53, and a second phase winding 55which is energized with a reversible phase relation through the loadwindings 56 and 56 of a magnetic amplifier 58. The load windings 56 and56 are disposed on magnetic cores 59 and connect the winding 55 to thetransformer 52 through oppositely disposed rectifier devices 60 and 61.The cores 59 are provided with opposing flux resetting windings 63,

and opposing pattern windings 65 which are energized from apilotgenerator G2 driven by the conveyor rolls 17 whenever the control relayCRL is deenergized.

Resetting of the servo motor system after passage of a sheet is providedfor by reset windings 66 which are connected between the moving contactFla and the intermediate point of a voltage divider comprising resistors*68 and 69 which are connected to a control source repre-' sented by theconductors 70. Feedback control windings 72 on the cores are connectedacross a pilot generator G1 driven by the servo motor under the controlof a reset relay LR, and oppose pattern windings 65. The relay LR isused in conjunction with a timing relay LRT to give a predeterminedreset period following operation of a screwdown control relay RL whichis utilized to connect the control windings 44 of the screwdown magneticamplifier 30 to the moving contact P3a of a potentiometer P3 which isenergized through a rectifier bridge circuit 75 in accordance with theoutput voltage of a 'synchro receiver 76 which is electrically connectedto a synchro transmitter 77 driven by the screwdown motor SDM.

The stator of the screwdown receiver 76 is manually ad justable tochange the phase relation relative to the transmitter 77, so that theoutput voltage of the receiver 76 is proportional to the separation ofthe rolls 11 and 12.

The other end of the control windings '44 is connected to' the movingcontact PM of a potentiometer P2 which is adjusted in accordance withthe initial thicknessSl of the sheet. The operation of the screwdowncontrol relay R1. is determined by a timing relay RLT and the controlrelay CRL. A timing relay TL and a sequence relay PL are used to set upthe operating circuit for the timing relay RLT so as to provide a singletiming interval as each sheet approaches the mill.

In order to provide for correcting for deviations due to an error in theinitial thickness S a length checking system 80 is provided for checkingthe length of the rolled sheet and correcting the position of thecontact arm P2a of the potentiometer P2 in accordance therewith. Thischecking is accomplished by utilizing control relays CR1, CR2 and CR3disposed along the conveyor on the exit or delivery side of the rollingmill and operated by phototransistors PT3, PT4, PTS respectively incombination with light sources LS3, LS4 and LS5, respectively. The lightsources LS4 and LS5 are set a distance on either side of an intermediatepoint indicated by dotted line 1 which is a predetermined sheet lengthfrom the light source LS3, which distance is slightly less than thenegative and positive tolerances respectively in the sheet length. Thefollowing sequence of events can occur:

(A) Relays CR1 and CR2 are not deenergized during a common interval oftime.

(B) Relays CR1 and CR2 are deenergized during a common interval of time.

(C) Relays CR1 and CR3 are not deenergized during a COHIIIIOIJ. intervalof time.

(D) Relays CR1 and CR3 are deenergized during a common interval of time.

Occurence of event A indicates off-length sheets on the short side,occurence of events B and C indicate on-length sheet and occurence ofevent D indicates off-length sheet on the long side. A scheme based onthe above sequences for determining whether a sheet is long or short isshown in FIG. 1C. A time delay relay T is used in conjunction with aprogram relay P and a coincidence relay C to permit relays S and L to becontrolled by the relays CR1, CR2 and CR3 to determine short and longsheet conditions. These relays in turn energize relays S and Lrespectively, for a timed interval determined by a timing relay DT foroperating a motor M in opposite directions to adjust the moving contactP2a to correct for the variation in sheet length.

If the light sources LS1 and LS2 are separated by a distance L and theorigin of time (i=0) is taken as the instant the sheet interrupts thefirst light source and I is the time as measured from this origin atwhich the first light source is restored, the length of the sheet isgiven by,

13 L1: f v dt For later convenience let t represent the instant thesecond light source is interrupted and the operation of the servocontroller initiated. Then t t; L f ll dt l f 111dt The first integralis, of course, given by,

f v dt=L L, wit

and if the servo system is linear and its response to a umt stepfunction input is represented by It T, then L; f v dt As previouslynoted, however,

Thus,

and hence,

r =L1 m The output voltage of the servo system, as seen from FIG. 1A, isgiven by,

The maximum length that can be measured by the system is given by,

LID: oi- 121+ 2 and hence,

The output voltage is consequently directly proportional to sheetlength.

Normally, relays CRL and TL are energized and relays PL, RLT, RL, LR andLRT are deenergized. When the sheet 48 interrupts both of the lightsources LS1 and LS2, the resistance of both of the phototransistors PTIand PT2 are increased and the relay CRL returns to the deenergizedposition. This connects the pattern winding 65 of the magnetic amplifier58'to the pilot generator G2 driven by the rolls through contact e ofrelay CRL applying thereto a voltage responsive to the speed of thesheet. This causes the magnetic amplifier 58 to operate the servo motorSM and position moving contact Pla in accordancewith the length of thesheet. Deenergization of relay CRL interrupts the energizing circuit forthe timing relay TL at contact member a of relay CRL, and completes anenergizing circuit for the operating winding of relay PL at contactmember b and sets up energizing circuits for relays RLT and RL atcontacts 0 and d respectively. Relay PL is picked up until such time asthe timing relay TL times out. Energization of relay PL completes anenergizing circuit for the timing relay RLT at contact member c of relayPL. The timing relay RLT operates to the energized position andcompletes an operating circuit for the screwdown control relay RL atcontact b. Operation of control relay RL connects the control winding 44of the screwdown magnetic amplifier 30 between the moving contact P311of potentiometer P3 and the moving contact P2a of potentiometer P2through contact a, so that the voltage e which is equal to e XL X kn,and is therefore proportional to the product of roll separation timesfinal length, or L XS is matched against the voltage e of potentiometerP2, which is proportional to the product of L XS Accordingly, thecontrol winding is energized in accordance with a differential betweenthe product of measured roll separation times final length and theproduct of initial length times initial thickness. This provides forenergization of the field windings 26 and 27 selectively, so as toenergize the screwdown motor SDM to raise or lower the rolls to theproper position to make the quotient of constant.

When the timing relay RLT times out, the control relay RL is deenergizedand disconnects the control windings 44 from the potentiometers. Acircuit is provided at contact member c of relay RL for a reset relay LRunder the control of a timing relay LRT. The relay LR provides a shuntabout a portion of a resistor 82 in circuit with the control winding 72,and connects the reset windings 66 to be energized in accordance withthe displacement of the potentiometer contact Fla. The magneticamplifier 58 thereupon functions to operate'the servo motor SM to returnthe contact arm Pla to its initial or its zero position.

When the rolled sheet passes through the mill, it then passes throughthe length checking system 80. In the absence of a sheet, relays CR1,CR2 and CR3 are energized. Program relay P is energized through contacta of relay T and contact member b of relay CR1. The relay P remainsenergized until the timing relay T, which is normally energized, timesout, at which time it returns to the deenergized position and remainsthere until the arrival of the next sheet. The momentary closure ofrelay P energises relay C and DT through contacts d and a thereof, bothof which provide holding circuits for themselves. If relay CR1 isenergized before relay CR2 is deenergized, as will be the case if thesheet is short, relay S will be energized momentarily through contact dof relay CR1 and contact a of relay CR2. An energizing circuit isthereby provided for control relay S through contact a of relay S untilthe timing relay DT times out. If relay CR3 is deenergized before relayCR1 is deenergized, as will be the case if the sheet is long, relay Lwill be energized momentarily through contact a of relay CR3 and contactc of relay CR1. This provides an enerigizing circuit for the controlrelay L which will seal in until the timing relay DT is deenergized andopens the circuit at contact a. Relays S and L thus selectively applyvoltages of opposite polarity to the motor M for a fixed interval oftime as determined by the timing relay DT, depending on whether thesheet is short or long. The motor changes the setting of potentiometerP2 to adjust the voltage e and hence the product L S E by a fixed amountin a direction for the ofi-length condition. The potentiometer P2 mayalso be adjusted manually and remote indication of its position shouldbe provided where it is available to the operator.

From the above description and the accompanying drawings, it will beapparent that I have provided in a simple and effective manner forcontrolling the length of rolled sheet. The roll separation isautomatically adjusted in accordance with the length of the sheetentering the mill and correction of the mill setting is antomaticallymade subsequent to rolling of the sheet in accordance with the measuredlength of the rolled sheet to compensate for errors including error dueto variation in thickness of the sheet. A sheet length controllerembodying the features of my invention provides for accurately rollingsheets, which, for example, may vary in.

7 thickness from .486 inch to .510 inch and in length from 29.953 inchesto 30.047 inches, to a predetermined length of 120.48 inches with atolerance of i2% Without incurring delays in the rolling process.

Since certain changes may be made in the above described constructionand difierent embodiments of the invention may be made Without departingfrom the spirit and scope thereof, it is intended that all the mattercontained in the above description and shown in the accompanyingdrawings shall be considered as illustrative and not in a limitingsense.

I claim as my invention:

1. In a control system for a rolling mill having a pair of rolls Withdriving means therefor and having a screwdown motor operable to vary thespacing of the rolls, the combination of regulating means operable toeffect operation of the screwdown motor, first signal producing meansactuated by the screwdown motor to produce a first signal in accordancewith the roll spacing, second signal producing means actuated by thepassage of a sheet of material toward the rolls for measuring the lengthof a sheet of material to be rolled and for producing a second signal inaccordance-therewith, and circuit means connecting the regulating meansand saidfirst and second signal producing means for applying a controlsignal to the regulating means in accordance with a differential betweensaid first and second signals.

2. A control system for a screwdown motor operable to vary the spacingof the rolls in a rolling mill having driving means therefor, controlmeans reversibly energizing said motor, sheet length responsive meansactuated by the passage of a piece of material of finite length to berolled for producing a first signal responsive to the length of saidpiece of material to be rolled, roll separation responsive meansresponsive to the position of the rolls for producing a second signal inaccordance with the separation of the rolls, and circuit meansconnecting the sheet length responsive means and the roll separationresponsive means to said control means for producing a signal responsiveto said first and second signals and applying it to thecontrol means foreffecting operation of the control means to energize said motor toposition said rolls.

3. Screwdown apparatus comprising, a motor reversibly operable andconnected to vary the spacing of the rolls of a rolling mill whichhave'driving means connected therewith, means operating said motorincluding a generator having a field winding and regulating meanstherefor having input and output circuits, sheet length sensing meansactuated by the passage of a piece of material of finite length forproducing a first signal in accordance with the initial length of apiece of material approaching the rolling mill, roll spacing sensingmeans actuated in accordance Withthe position of one of the rolls forproducing a second signal in accordance with the spacing of the rolls,first circuit means connecting said sheet length and roll spacing meansto said input circuit for applying said first and second signals to theinput circuit of the regulating means in opposed relation, and secondcircuit means connecting said output circuit and the generator field foreffecting operation of the motor to adjust the roll spacing to maintainthe quotient of initial length final thickness substantially constant.

4. screwdown control apparatus for a rolling mill having a pair of rollswith driving means for at least one of 'said rolls comprising, a motorconnected in operating relation with one of the rolls of the rollingmill for vary-.

a signal in accordance with the length of said sheet, first circuitmeans including a voltage divider connected to multiply said signal by aquantity proportional to the initial thickness of the sheet, secondcircuit means including means actuated by one of the rolls to produce asignal proportional to the roll separation and a second voltage dividerconnected to produce a signal in accordance with the product of thelength and thickness of the rolled sheet, third circuit means connectingsaid first and second circuit means and the regulator for applying thesignals produced by said first and second circuit means to the regulatorin opposed relation for operating the motor in accordance with adifferential therebetween, and additional circuit means connecting theservo systems for operating the servo system in accordance with thelength responsive signal for resetting the servo system after thepassage of a sheet.

5. In a sheet length control for a rolling mill having a pair of rollswith driving means therefor and screwdown means operable to vary theseparation of the rolls, a screwdown motor operable to operate thescrewdown means, sheet length responsive means actuated by the passageof a sheet approaching the mill to produce a first signal responsive tothe length of a sheet approaching the mill in response to passage of thesheet, roll separation responsive means actuated by one of the rolls forproducing a second signal in accordance with the roll separation,regulating means connected to control the operation of the screwdownmotor, circuit means connecting the roll separation and sheet lengthresponsive means to the regulating means to make the regulating meansselectively responsive to a differential between said first and secondsignals for reversibly operating the screwdown motor to maintain apredetermined relation of the initial sheet length and the rollseparation, second circuit means including means actuated by the passageof a sheet leaving the mill operable to produce a third signal inaccordance with the length of a sheet departing from the rolling mill,and control means operated by the last mentioned third signal andconnected to modify a predetermined one of said first and second signalsin response to the variation of length of the rolled sheet fiom apredetermined value.

6. In a sheet length controller for a rolling mill having a pair ofrolls with driving means therefor and screwdown means for varying theroll separation, a screwdown motor operable to actuate. the screwdownmeans, sheet length sensing means including a speed matching servosystem actuated by a sheet entering the mill to produce a first voltageproportional to the length of a sheet of material entering the mill,roll separation sensing means including a selsyn device operated by theposition of the screwdown motor for producing a second voltageproportional to the separation of the rolls, regulating means having awinding connected to be energized by the difference between said firstand second voltages and connected to eifect energization of thescrewdown motor to adjust the roll separation, means operated by theservo system producing a signal in response to operation of the servosystem, circuit means applying said signal to reset the servo system,sheet length checking means actuated by the passage of a sheet leavingthe mill to check the length of a sheet leaving the rolling mill, andmeans including apotentiometer connected in circuit with the servosystem and operated by the checking means to modify said voltage signalapplied to the regulating means from the servo system. a

7. In sheet length control apparatus for a rolling mill having a pair ofrolls with driving means therefor and screwdown means for varying theroll separation, a screwdown motor connected in driving operation withthe screwdown means, a regulator connected to control .the operation ofthe screwdown motor, circuit means connected to produce and apply to theregulator a first voltage in accordance with the speed of the screwdownmotor, circuit means connected to produce a second voltage in accordancewith the separation of the rolls, means including a voltage dividerconnected to apply a predetermined portion of said second voltage to theregulator, means including a servo system operated by the passage of asheet approaching the mill for producing a third voltage in accordancewith the length of a sheet of material to be rolled, and circuit meansfor multiplying said second and third voltages including a voltagedivider connecting the regulator and the servo system to apply apredetermined portion of the third sheet length voltage to the regulatorin opposition to the second roll separation voltage.

8. Control apparatus for a rolling mill having a pair of rolls withdriving means therefor and screwdown means for varying their separationand comprising, a screwdown motor connected in driving relation with thescrewdown means, a regulator connected to control the operation of saidmotor, circuit means including a pilot generator driven by the screwdownmotor connected to apply to the regulator a first voltage in accordancewith the speed of the screwdown motor, means including a synchro systemoperated by the screwdown means to pro duce and apply to the regulator asecond voltage in accordance with the separation of the rolls foroperating the motor to reduce the separation of the rolls, meansincluding a servo system operated by the passage of and responsive tothe speed of a sheet of material entering the mill to produce a thirdvoltage in accordance with the length of the sheet, circuit meansproducing a fourth voltage proportional to the thickness of a sheetentering the mill, and additional circuit means comprising a voltagedivider connected to the servo system and the regulator to apply to theregulator a predetermined portion of the sheet length third voltage soas to multiply the length third voltage and the thickness fourth voltageand to apply the resultant to the regulator in opposition to the rollseparation second voltage.

9. Sheet length control apparatus for a rolling mill having a pair ofrolls with driving means therefor and screwdown means operable to varythe separation of the rolls and comprising, a screwdown motor connectedin driving relation with the screwdown means, a regulator connected tovary the energization of the motor for controlling the operation of thescrewdown motor, circuit means including a pilot generator driven by thescrewdown motor and connected to apply to the regulator a voltage inaccordance with the speed of the screwdown motor, means including asynchro transmitter and receiver operated by the screwdown motor toapply to the regulator a first voltage in accordance with the rollseparation, means including a servo system having a motor responsive tothe speed of a sheet of material entering the mill for operating a sheetlength potentiometer connected to a source of control voltage to producea second voltage in accordance with the length of a sheet of materialentering the mill, a thickness potentiometer connected in cascade withsaid sheet length potentiometer for applying a predetermined portion ofthe second volt age to the regulator in opposition to the rollseparation first voltage, sheet length checking means operated by asheet leaving the mill to check the length of the sheet leaving themill, and means operated by the length checking means and operable toadjust the thickness potentiometer in accordance with variations in thefinal sheet length of a sheet already rolled to correct the length ofthe next sheet to be rolled.

References Cited in the file of this patent UNITED STATES PATENTS2,051,018 Umansky Aug. 11, 1936 2,297,812 Stoltz Oct. 6, 1942 2,332,573Hibschman Oct. 26, 1943 2,476,839 Cook July 19, 1949 2,687,052 ZeitlinAug. 24, 1954 2,851,911 Hessenberg Sept. 16, 1958 FOREIGN PATENTS627,000 Great Britain July 25, 1949

